Adaptive circuits are well known and used in a variety of applications. One well-known example of an adaptive circuit is the feed forward amplifier (“FFA”). In order to achieve linearity in a feed forward amplifier, careful control of the amplifier circuitry is required. In particular, in FFAs two or more gain and phase adjusters are often employed and the taps of each of these adjusters are carefully steered to achieve linearity through the amplifier.
Within the art of FFAs, it is known to use detector-controller circuits, one for each gain-and-phase adjuster. Each detector-controller circuit is operable to steer the taps of its respective gain-and-phase adjuster in the FFA so that the main amplifier and correctional amplifier can properly cooperate in order to reduce error introduced by the main amplifier and, should a pilot tone be used in the FFA, to also reduce the output residue of the pilot tone injected prior to the main amplifier.
In certain prior art detector-controller circuits, once the detector portion of the detector-controller circuit has indicated that the associated controller portion should make an adjustment, the controller arbitrarily steers the taps of the gain-and-phase adjuster in a direction to either increase or decrease the input to the tap, without knowing which of an increase or decrease will actually achieve the desired effect. In order to verify whether the controller steered the tap in the correct direction (e.g., to increase the signal to the tap), after the correction has been applied the detector circuit ascertains whether the direction of the variation brought about the desired effect, and, if so, instructs the controller circuit to continue steering in the same direction, if necessary. If, however, the detector circuit ascertains that the steering direction brought about an undesired result, then the detector instructs to the controller to try steering the tap in the opposite direction (e.g., to decrease the signal to the tap).
In the prior art, each detector-controller circuit works independently of each other, and therefore, achieving convergence towards an optimum level for each tap of each adjuster can be difficult. For example, rapid changes in the strength of the input signal being amplified by the FFA can make it difficult for the detector-controller circuits to respond quickly enough to converge the tap levels of each gain-and-phase adjuster towards the respective optimum levels. Furthermore, the adjustment of one tap of a gain-and-phase adjuster can disrupt an optimum or near optimum input level achieved at another tap, therefore cascading disruptions through all of the taps.
The inventor of the present invention also believes that a further problem is that such prior art controller circuits can sometimes result in taps being steered to levels that are levels corresponding to local minima for the input signal, missing a global optimum for the input signal.